Linear motion guide units have been extensively applied in recent years between relatively sliding parts for linear reciprocating mechanism used in increased industrial fields including semiconductor fabricating equipment, machine tools, industrial robots, and so on. Most prior linear motion guide units have been ordinarily fed with lubricant at regular intervals through any oiling port to ensure smooth lubrication for the rolling elements throughout a circulating circuit. Recently advanced machines and instruments, nevertheless, are increasingly needed to make them virtually maintenance-free from many aspects of conserving energy as well as keeping running cost and maintenance cost of equipment reasonably less than ever. Correspondingly, the linear motion guide units incorporated in the advanced machinery, especially the linear motion guide units of the sort applied between relatively sliding parts for linear reciprocating mechanism, are also challenged to keep down the consumption of lubricant to a minimum, along with realizing virtual maintenance-free operation where lubricant resupply is less needed over long-lasting operation. With the linear motion guide units constructed as stated earlier, continuous application of lubricant around the rolling elements is indispensable to continue maintaining an adequate lubricant film around the rolling elements to keep them against metal-to-metal contact while rolling through the circulating circuits, thereby making sure of their high durability.
In Japanese Laid-Open Patent Application No. 2008-111, 458 which is a commonly-assigned senior application, there is disclosed a linear motion guide unit having a guide rail of a matter of 10 mm in width and more than one very small or miniature roller of 1 mm or so in diameter. With the prior linear motion guide unit constructed as stated earlier, a retainer plate to support the rollers in a load-carrying race and end caps are joined together each other to provide an endless circulating circuit with no gap to allow the rollers smoothly rolling through there with keeping adequate posture. A slider has a carriage, end caps, rollers rolling through the endless circulating circuits, the retainer plate extending along the load-carrying races on the carriage to keep the rollers inside the load-carrying races, and a binding strip to fasten the retainer plate to the carriage. The retainer plate at lengthwise ends thereof is coupled together with spigots extending out of the end caps to communicate turnaround passages in the end caps. The spigots conform complementarily to the lengthwise ends of the retainer plate to fit over the lengthwise ends of the retainer plate. Especially, butting extremities of the retainer plate and the associated spigots are made beveled ends in complementary relation to one another aslant in the sliding direction.
In another Japanese Laid-Open Patent Application No. 2008-82, 433 which is a commonly-assigned senior application, moreover, there is disclosed a linear motion guide unit in which application of lubricant around the rolling elements was done at the turnaround passage to make the lubrication system simpler than ever in construction, along with maintenance-free for steady and positive oil lubrication. With this prior linear motion guide unit, a porous compact impregnated with lubricant fits into a concavity made on an outward end surface of the end cap. The concavity is deep pitted to open into the turnaround passage in the end cap. The porous compact impregnated with lubricant is placed in the concavity in the end cap in such a way as to expose in part itself to the turnaround passage through the deep pit. Thus, the porous compact makes contact with the rolling elements running through the turnaround passage to come to supply with the lubricant around the rolling elements.
With the prior linear motion guide unit constructed as stated earlier, the resupply of lubricant is done through the grease nipple into the turnaround passages in the end cap, but wouldn't be applied directly to the porous compact impregnated with lubricant.
In Japanese Laid-Open Patent Application No. 2011-149, 469 which is also a commonly-assigned senior application, there is disclosed a linear motion guide in which the porous compacts impregnated with lubricant are installed in the recesses inside the inward end surfaces of the end caps facing each other or opposite to the forward and aft end surfaces of the carriage to is between the end caps and the carriage. With this prior linear motion guide unit, the porous compact impregnated with lubricant is fitted into the recess in a fashion exposed in part to the turnaround passage through an opening in the turnaround passage so that the rolling elements rolling through the turnaround passages, as coming into rolling-contact with the part of the porous compact exposed out of the opening, are applied with the lubricant.
With the prior linear motion guide unit constructed as stated just above, however, the resupply of lubricant is done through the grease nipple into the turnaround passages in the end cap. Oiling paths for lubricant reaching the turnaround passages are defined by the end caps and the porous compact impregnated with lubricant. The resupplied lubricant at the grease nipple is absorbed in the porous compact while getting in contact with the porous compact in the oiling paths. Thus, the prior linear motion guide units with grease nipple have need of a lubrication port structure with female threads to fit over the grease nipple. Because the lubrication port structure takes up a considerable space, it is inevitable to make the porous compact impregnated with lubricant less in volume and, therefore, making the end cap large in size enough to accommodate the grease nipple.
Meanwhile, with the miniaturized linear motion guide unit in which tiny rollers are built as a four-row array around the guide rail having a width of for example 12 mm, our experts have ever tried doing the lubrication for the rollers at the turnaround passages in the end cap with using the porous compact lying on the outward end surface of the end cap in the face of the end seal, the porous compact having a lubricant reservoir, whose a part protrudes to be exposed in the turnaround passage through the opening pitted in the end cap.
On the other side, the linear motion guide unit constructed as stated earlier normally has a binding strip to fasten a retainer plate to the slider to keep the rolling elements against falling away from a load-carrying race, and for the sake of which the end cap on its outward end surface facing on the end seal has grooves into which the bent ends of the binding strip fit to make snap-engagement with the associated end cap. Because the grooves to retain the binding strip take up a large space across the outward end surface of the end cap and further there is no space for the provision of the grease nipple in the end cap, it is impractical to make the porous compact large in volume at either side of the lubricant reservoir and the applicator nose coming into contact with the rolling elements. It was found that making the porous compact excessively large in volume would render overall the linear motion guide unit worse or less in mechanical strength. Moreover, the applicator nose of the porous compact, as undergoing repeated collisions with the rolling elements, is needed to have a mechanical strength enough to stand up to repeated impacts caused by the rolling elements.